Hi...It is a Micro-wave Doppler effect sensor. The principle is simple : it sends microwave and does the difference between the sended wave frequency and the response wave frequency.The difference of frequency is proportionnal to the speed of the object it detects.But, as you might expect it, I have a problem : I've spent some time working on the output signal, it's a sine signal which amplitude is around 10 to 100 mV depending on the size and the distance of the object.My problem is that I can't find a SIMPLE solution to amplify this signal in order to use it with an Arduino. I've tried several Amp Op such as LM381 or TL082 but with no luck : the LM381 doesn't work with AC signals and the TL082 seems to not detect the input signal

It will give you an amplifier with 10 times voltage gain. If you replace the 100k resistor between input and output with a 1Mohm type your gain will go up to 100times.I belive that you probably need to power the OP amp with more than 5V. 12V is more suitable.Once you get this working you can start looking for low voltage OP amps if you want to power the amplifier from 5V.

As an alternative if you are not that comfortable working with analog circuits you can use the cicuit below that uses a single 74HC04 gate.The feedback resistor forces the gate in to its analog region and creates an amplifier with lots of gain. In fact it has so much gain it will probably oscillate without input signal. But once you have a few millivolts of signal it will amplify it cleanly.Should work well driving from 5V,